AceShowbiz - Emmy Rossum is leaving Shameless after playing Fiona Gallagher on the show for eight years.

The actress announced the surprise news in a lengthy Facebook post on Thursday, August 30, revealing she knows she's going to struggle when her run of the drama ends.

"It's a hard thing to put into words, feelings," she writes. "But I'm going to try... Until Shameless came into my life 8 years ago, I led that kind of transient wonderful life of an actor. And I never realized how much I actually craved the kind of continuity that this show has given me. And given all of us in the crew.

"Season after season I'm amazed that our same crew comes back. And it's not just because it's a wonderfully written, wonderfully layered show. There are these real connections, real friendships that bring us back season after season after season...".

Emmy explains growing up as an only child made her "dream of" having a large family like the one she has found on the set of the show with her crew and castmates, including TV dad William H. Macy.

"In real life, unlike Fiona, I'm an only child," she continues. "I never had a big family. Being ensconced in that messy Gallagher family love is something I'd always dreamed of. But even off set, it feels real... This kind of stability, this family, has nurtured me and made feel safe enough to stretch and grow creatively...".

"The opportunity to play Fiona has been a gift," she adds. "There are few characters - female or otherwise - as layered and dynamic... Quite simply, the last eight years have been the best of my life... I know you will continue on without me, for now. There is much more Gallagher story to be told. I will always be rooting for my family. Try not to think of me as gone, just think of me as moving down the block."

It is unclear why the actress is leaving the hit drama, but her departure comes almost two years after it was reported she was ready to walk away following a pay dispute.

Season nine of the show will premiere on 9 September on American network Showtime.